Learning Forum

[Payam Mashinchi Abbasi]

Hi,

I want to get the extinction cross section or efficiency vs incident angle graph for a cylinder. I have used TFSF source and PML boundary conditions and tried to get scattering and absorption cross section and sum them up to get the extinction cross section but the scale of results are not correct and it did not change by changing the angle. Is there any problem with normalization and units? How can I solve this problem?

[Guilin Sun]

Is this single wavelegth or broadband?  

for single wavelength, the result should change with angle Theta, but not necessarilly with phi if theta is zero (if source injection is along the symmetrical axis) , since it only changes the polarization direction.

For broadband, TFSF source currently does not support it as the incident angle changes with wavelength, the same as plane wave.

You can do two simulations with and without the scatter and post process the scattering by field difference.

 

You said that the result is not correct, do you mean the result does not change with angle? please make sure the source angle is set correctly, mainly the theta angle. in addtion, make sure the simulation volume, TFSF region and the analysis group dimension are proper.

 

If there is still no improoment, please post some screenshots about the settings.

 

 

[Payam Mashinchi Abbasi]

Thank you for your response. My simulation is for a single wavelength and the source injection is normal to the symmetrical axis of the cylinder as shown in the previous image. I got the sweep results of scattering cross section for 3 different wavelengths as below:

and the analytical solution for extinction efficiency must be similar to below graph:

what should I do to get the same results? Meanwhile, how can I calculate the extinction efficiency, directly?

[Guilin Sun]

For extinction efficiency, please check its definition. Maybe it is simply normalized with geometry cross section.

It is uderstandable that you want to have the same result. However do you know the polarization the reference used? is it linear or circular or elliptical ?

Cross sections for absorption, scattering and extinction simulated by FDTD have been verified with theory. Therefore please check carefully the settings and the reference. I have a post which lists a dozen of issues to be checked: 

Ansys Insight: Why my simulation result is different from published paper or experiment?